The present invention relates generally to a crank angle detecting device for an internal combustion engine. More particularly the invention relates to the crank angle detecting means adapted to process crank shaft angular position data for precisely detecting a timing, such as fuel injection timing and/or spark ignition timing, with respect to a crank shaft reference angle.
In an electronic engine control, it is essential to detect the timing parameters in relation to a crank shaft angular position. In order to detect the crank shaft angular position, the crankshaft is equipped with a crank angle sensor for producing a pair of crank angle signals. In general, the crank angle sensor is adapted to produce a crank reference signal at predetermined crank shaft angular positions, e.g. at every 90.degree. or 120.degree. depending on the number of cylinders in the engine. The crank angle sensor is further adapted to produce a crank position signals at predetermined crank shaft rotational angles, e.g. 0.5.degree. or 1.degree..
In view of the manufacturing cost, a crank angle sensor producing only the crank reference signals is preferred when such crank angle sensor is used. In this case, the intervals between the crank reference signal are measured by means of a clock. The average rotational speed of the crankshaft is calculated on the basis of the measured interval and the predetermined crank shaft rotational angle to produce the crank reference signal. The crank shaft angular position at a certain timing, such as fuel injection timing and/or spark ignition timing, can then ba approximated, from the calculated average rotational speed and the measured period.
However, if the engine is in a state wherein cycle-to-cycle fluctuation of engine speed is significant, such as during cranking or the engine warm-up period, errors between the actual crank angle position and approximated value become unacceptably great. In particular, if the engine is a diesel engine which tends to fluctuate significantly even during one cycle of engine revolution, the error between the actual crank angle position and the approximated value will be significant. This leads to errors in timing control, such as fuel injection timing control and/or spark ignition timing control, which in turn may cause increase of exhaust emissions or engine noise, poor fuel economy or degradation of drivability.
On the other hand, reduction of emissions and engine noise and improvement of fuel economy are all quite necessary nowadays. This requires more precise control of engine processes. To control engine operation more precisely, the crank shaft angular positions as crucial timings, such as fuel injection timing, spark ignition timing and so forth, must be determined accurately.